Rudyard Kipling, in his poem “IF-” has given some definitive guide to build a sound character. Developing humbleness is a part of that. It is the quality of having a modest or low view of one’s own importance. According to the poet, we should not show off ourselves as too good a person or talk too wisely with common people, even after possessing good qualities. 

And yet don’t look too good, nor talk too wise

If we are not humble, people would feel uncomfortable in our company and avoid us, hindering our chances of success in life.